In recent years, the optical disc has been used more and more extensively to store video information thereon. Thus, to record a video of even better quality thereon for a longer time, further increase in recording density and read/write speeds thereof is strongly demanded. To achieve this purpose, it is naturally effective to develop a novel storage medium on which information can be stored at an even higher density. However, it is equally important and pressing as well to reduce a so-called “overhead area” (e.g., address area), not contributing to increase in the capacity of information to be stored, as much as possible.
FIG. 13 illustrates a format for an information track on a conventional optical disc. In FIG. 13, the reference numeral 1501 denotes a sector as an information unit, the reference numeral 1502 denotes a non-rewritable header field recorded in the shape of pits while the optical disc is manufactured, and the reference numeral 1503 denotes a recording field on which information can be written.
In the conventional optical disc, each track has a format in which a number of sectors 1501 are arranged in line as minimum read/write units. Each of these sectors 1501 consists of a header field 1502 having a length of 128 bytes and a recording field 1503 having a length of 2,569 bytes.
Although not shown in FIG. 13, the recording field includes a VFO (variable frequency oscillator) field, a data field on which user data is written, and a buffer field as a redundancy area. The VFO field is provided to accomplish a phase lock on a PLL (phase-locked loop), which is needed for reading out a signal recorded.
In the conventional optical disc, to specify what sector on what part of the disc a light beam spot is now following, each header field 1502 includes location information (i.e., address information representing a specific location on the optical disc). The location information stored on the header field 1502 indicates the location information of the sector 1501 including the header field. More specifically, as shown in FIG. 13, location information “123456” has been recorded on the header field of the sector 1501 specified by an address “123456”. This location information has a length of 4 bytes. An error detection code of 2 bytes is added to the 4-byte location information to see if the location information has been read out correctly.
A signal representing the location information is recorded at the same density as the data to be written on the recording field. Accordingly, the signal, as well as the data, needs to be read out using a PLL. For this purpose, a VFO field is also provided for the header. When an optical disc is used as a peripheral storage device for a computer, the information stored on the optical disc should be much more reliable as compared to a situation where the same optical disc is used to record or replay video or music on/from it. Thus, to consolidate the reliability, the same location information is recorded four times on a single header. As a result, the location information per header has a total length of 128 bytes.
As described above, in the conventional optical disc, each sector has to store the same location information thereon physically four times and also needs a so-called “overhead area” such as a VFO field. Accordingly, the storage capacity of the optical disc decreases correspondingly.
In order to overcome the problems described above, the present invention was made and its object is to provide an optical disc that includes a smallest possible overhead area and can be used effectively to store video or any other type of information thereon, and an optical disc drive for such a disc.